Auxiliary diagnostic apparatuses include magnetic resonance (MR) systems, ultrasonic systems, computed tomography (CT) systems, positron emission tomography (PET) systems, nuclear medicine and other types of imaging systems.
For example, during CT X-ray imaging of a patient by a CT system, X-rays are used for imaging the features of inner structures and regions of interest (ROI) of the patient body. The imaging is performed by a CT scanner. In operation, an object is scanned for collection of original data; then an image is reconstructed after the original data are preprocessed; and post processing is further performed to improve quality of the image.
Due to spectral correlation of ray attenuation performance of a real object, in the case of polychromatic X-rays, it will be viewable that average energy of X-rays emitted by a penetrated object shifts to a higher energy value. This effect is called “beam hardening”. In a reconstructed image of the object, linear and spectrum-related ray attenuation can be observed via shift relative to grey scale value in a theoretical case. Especially, grey scale value shift in the reconstructed image caused through high nuclear charge number and high-density material (such as bone) or a beam hardening virtual image causes the reconstructed image to interfere with correct judgment of the image and may cause a relevant doctor to misinterpret the image in a worst case.
In preprocessing, beam hardening correction is carried out to at least partially eliminate the virtual image. Some existing beam hardening techniques have exhibited improved uniformity for aligned scan; however, for eccentric scan, the image still shows a band-shaped artifact.